This isn't a review, just final thoughts on the story now that it's over.
Basically, I only took interest in Gosick for the mystery. I was done for the moment with Umineko and was seeking for another show that would keep me entertained with mysteries to resolve. What I found was a show that had various small not-of-my-liking mysteries that were resolved too quickly and didn't let the viewer think. It was an anime that just showed mysteries for the lulz, it never attempted to give anybody a challenge. The mysteries were resolved in the same episode as they were presented. Victorique was just script-reading, she took small things and made unrealistic explanations out of that that explained what had happened.
It felt the show cheated you - you weren't given true tools to solve stuff. Or time for the matter. It was a show that tried to give you mysteries for the lulz. After a while, it became a show that didn't know what to do. And then, somehow, some mysteries that kinda sucked started to slowly create the universe of Gosick. The relationship between Victorique and Kujo also became a big focus of the show. At first, I was worried. I felt the show had realized it sucked at mysteries and was focusing on the characters for not sucking entirely. But in the end, that was a good move.
Finally, the arc regarding the Mystery of the Leviathan was the best episodes of the show. It truly elevated this show, even if the rushed ending would then bring it a bit down. I mean, episode 23 came out of nowhere, was very rushed, and made no sense overall. Finally, the ending was pretty much perfect for me. An average show that ended in a splendid way. 7/10 for me.